• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.7
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• pp.905-910
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• 2010

Exhaust manifolds are the first structures to be developed by hydroforming; mass production of exhaust manifolds by this method will be possible soon. This is obviously related with tight emission regulation induced by environmental problems commonly for both domestic and worldwide and standards, thus evoking its solution for domestic automakers. Compared to conventional cast products, thin-gauge tubular hydroformed exhaust manifold have superior features; for example, in the hydroformed exhaust manifold, gas decomposition during the cold-start period of the engine is reduced by lowering the heat sink, and manufacturing process is simplified since less welding is involved. The aim of this study is to develop a hydroformed exhaust manifold; the study deals with the components, the hydroforming process, and tool design of the manifolds. The performance of the exhaust system is evaluated by performing flow analysis, heat-transfer analysis, heat-stress analysis, and fatigue analysis by using a computer.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.19 no.2
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• pp.163-170
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• 2010

We have studied on welding dissimilar materials of cold-reduced carbon steel sheet and stainless steel sheet together by using laser beam. It is well known that stainless steel is so strong againt rust and heat, while cold-reduced carbon steel is widely used in various parts of industry. In this research we have performed some experiments to know the possibility of welding dissimilar materials using laser beam by adjusting the power output of 3kW laser. Other conditions of the experiments were as follows : the welding speed was varied in the range between 2m/min and 7m/min, argon gas and helium gas were used as shield gas, the flow value of shield gas was ranged between $10{\ell}/min$ and $30{\ell}/min$, and the gap of two materials was ranged between 0mm and 0.3mm. In order to ascertain of the welded surface, we have done the tensile strength testing, the hardness testing and the microscope observation. As a result, we have found that tensile strength was the highest at the condition of the welding speed of 4, the flow value of $20{\ell}/min$, the gap of two materials 0, and the use of helium gas. Above testings have also showed that the tensile strength was generally satisfactory since the penetration of welding was almost complete due to the thinness of the materials. In addition, the formation of the welded area was excellent when it had the highest tensile strength.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.3
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• pp.291-298
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• 2010

A conventional EGR cooler, which is used in an EGR system of an automobile diesel engine, has a low heat-exchange efficiency. To maximize the heat transfer between the exhaust gas and coolant, dimples are formed on the surface of heat exchange tubes. When designing the dimpled EGR cooler, the net heat transfer areas in the conventional and dimpled tube-type EGR coolers are compared. Structural integrity evaluations are also performed by combining finite element analysis with a homogenization method. Subsequently, the process of manufacturing the dimpled tube, i.e., the formation of dimples, edge bending, center v-notch bending, compression, and plasma welding, is established and carried out. Thus, the dimpled EGR cooler is developed, and its performance is verified.

• Corrosion Science and Technology
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• v.9 no.6
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• pp.331-337
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• 2010

This study compared the macro and micro electrochemical characteristics at the local area of welding metal on dissimilar welding parts for type 304 stainless steel (SS) and type 316L SS. The materials are used for double wall gas pipe of duel fuel engine for a ship. The various potentiodynamic experiments were performed several times in 10% ${H_2C_2O_2}{\cdot}{H_2O}$ solution using macro and micro methods, respectively. The micro electrochemical experiments conducted to resolve at local area on cross-section of dissimilar welding materials by micro-droplet cell device. The micro-droplet cell techniques can be used almost electrochemical experiments to resolve corrosion characteristics of the limited electrode area of the metallic surface between wetted spot of working electrode and tip of sharpened capillary tube. The results of macro electrochemical experiments show that resistance of active dissolution reaction at welding zone was high due to low current density by formation of passivation protection film at passive region. According to the micro electrochemical experiment, the corrosion current density of welding zone and bond zone were relatively high.

• Aerospace Engineering and Technology
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• v.12 no.1
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• pp.40-45
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• 2013

Satellite's infrared detector shall be calibrated under thermal vacuum environment using a reference black body before a launch. The full aperture black body (FABB) as an infrared calibration reference shall be composed of vacuum compatible materials and temperature controlled from $-40^{\circ}C$ to $+40^{\circ}C$ with emissivity higher than 0.95. The temperature homogeneity over the central 80 % area of the FABB front surface shall be better than 2 K. The FABB designed by thermal and flow analysis was $1m{\times}1m{\times}8mm$ copper plate on which black painted aluminum honeycomb core was attached. Copper tubes were welded on the opposite side of the honeycomb core to allow temperature regulated gaseous nitrogen to flow through them. By the FABB validation test, the temperature homogeneity was observed around 1 K using 20 PT100 sensors and modified COTS infrared camera. The emissivity value was 0.975 at $40^{\circ}C$ under atmospheric pressure.